If a Telco were permitted to sell services over the counter, no ID requirements, just a straight transaction. $100 cash for 12 months of mobile service. "Here's the SIM and the number, have a nice day"; they would. There'd be customers lined up around the block.
That's how it was when I arrived in Korea back in the late 90's. You could buy a phone almost anywhere, or someone leaving country sell you their used phone. Then all you had to do was buy a minutes card from any store.
Doesn't matter now. You might be on the run from domestic abuse. Can't have a service without providing a Telco with your full name, email, home address etc.